Different methods of taking in a fish catch from a cod end are known.
In one method, the cod end is hauled from the water with the catch along a stern ramp on the vessel. If, however, the catch is large, it will be damaged by the compression during the towing.
In a second method, the so-called Norwegian method, the cod end is hauled alongside the vessel in the sea, after which a fish pump from the vessel is fitted on the cod end so that the catch can be pumped on board. The disadvantage of this method is that it can only be performed in relatively calm weather since the bag in rough weather would start to sink, because the buoyancy of the fish is impaired.
In order to overcome these shortcomings, it is known from EP-PS no. 73,769 to arrange a fish pump on a cod end and via a pump hose to pump up the catch while the cod end remains in the sea. For this purpose a radial pump is used having a gate valve fitted in the inlet channel of the pump for opening and closure of the influx of fish to the pump. Moreover, water inlet openings are provided in the channel so that the pump at the beginning when the valve blocks the admission of fish can pump clean sea water, after which the valve is opened and the pumping up of the catch can begin.
However, this known fish pump has the disadvantage that the admission of fish to the pump cannot be adjusted without risking to damage the fish when they pass the valve if the valve is not completely open. Add to this the condition that there is no opportunity for adjusting the water amount between each fish in that the water inlets are permanently open. This means that, in particular, large fish are damaged because they require a larger water volume relative to the fish volume if damage during pumping is to be avoided. Finally, the pump is a radial pump with an outflow direction being inexpedient since this may result in the pump hose being bent so sharply that the flow conditions are badly impaired resulting in possible damage to the fish.